Beta Subreddits

Tech Subreddits

Content Philosophy

Content which benefits the community (news, rumors, and discussions) is valued over content which benefits only the individual (technical questions, help buying/selling, rants, etc.). This fundamental difference in audience is why we support two communities, r/Apple and r/AppleHelp. If you'd like to view their content together, click here.

Let me try to explain it:
When you want to restore (flash) your iPhone software, iTunes first contacts the Apple server to ask whether the version you want to use is actually the latest version. Apple does this to prevent people from downgrading their iPhone's.

The response from Apple's servers is unique for your iPhone and the version you want to restore. The response is called an "SHSH". Apple only gives permission for the most recent version at that moment, which is why you can only save the latest SHSH available.

What hackers did in a response to this was to "ask permission" to restore the currently highest version from Apple, and then store that SHSH on their own server. With a very simple modification to a Windows file on your computer (hosts), iTunes will contact the hackers server instead of Apple's server.

You need to give permission to the hackers for them to store your SHSH on the hackers servers, as otherwise they might be sued for storing "personal data".

To get as much people as possible to store their SHSH's, they put it on the front page of Cydia: every time a new firmware comes out, the front page of Cydia will transform into a "Make my life easier!" button with some text. Tapping this will save your SHSH of the newest version available at that moment. You can also manually save your SHSH and check which SHSH's you have saved at any time using a nice little app called tinyumbrella.

I assume they need an 4.2b3 SHSH because their latest hack contains some code from that version, and the iPhone won't accept it without the SHSH.

You actually don't have to install a firmware to get the SHSH for that particular version, Apple jut has to be giving them out for it (meaning it always gets the SHSH for the current newest official firmware). Cydia obtains and stores the current SHSH no matter which version you're on.